In the state of the art, test systems are known which are used for testing a device under test such as a communication device, for instance a 4G or 5G communication device. The test system usually comprises an antenna array which has a plurality of individual antenna elements used to emit electromagnetic waves. The individual antenna elements are controlled such that whole antenna array is deemed to be one single antenna element emitting one electromagnetic signal having certain characteristics. Accordingly, phases and amplitudes of the electromagnetic waves emitted by the individual antenna elements are adjusted appropriately.
Generally, the test system can be used to test the device under test under far field conditions inside a small test chamber of the test system. It is known that far field conditions correspond to electromagnetic signals being plane waves. Hence, antenna arrays have to be provided which can emit plane waves at the location of the device under test. Usually, the device under test is positioned in the near field of the antenna array. Thus, the antenna array has to emit plane waves in its near field in order to ensure that far field conditions can be tested. Therefore, the antenna elements of the antenna array are controlled such that they generate electromagnetic waves which together form a plane wave at the location of the device under test, for instance. Then, it is possible to measure and analyze the receiving and transmission properties of the device under test under far field conditions even though a small distance is provided between the antenna array and the device under test.
Usually, the arrangement of the plurality of antennas within the antenna array is provided such that optimal performances are obtained for a certain test condition. Accordingly, the antenna array is suitable for a specific application, in particular a certain distance between the antenna array and the device under test which in turn corresponds to a certain frequency of the plane wave and/or a specific size of the device under test.
However, the user of such a test system also wants to test different devices which may have different sizes and/or test the same device with different frequencies. Thus, another antenna array has to be installed and calibrated in order to perform these further tests being of interest. This results in a lot of additional effort which in turn increases the costs of the measurements.